Polymerizable boric compounds, methods of producing the same, polymerizable compositions and ionic-conductive polymeric electrolytes

ABSTRACT

A polymerizable boric compound for electrochemical devices represented by the formula (1), wherein, B represents a boron atom, Z represents a polymerizable functional group, X represents a divalent C 1-12  hydrocarbon group or in the absence of X, Z and B form a direct bond, AO represents a C 2-4  oxyalkylene group, m and n are each the number of moles of the oxyalkylene group added and each independently stands for 2 or greater but less than 6, and R 1  and R 2  each represents a C 1-12  hydrocarbon group.

CLAIM OF PRIORITY

This application claims priority from Japanese application serial No.2004-365760, filed on Dec. 17, 2004, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to polymerizable boric compounds forelectrochemical devices, methods of producing the same, polymerizablecompositions, and ionic-conductive polymer electrolytes.

BACKGROUND OF THE INVENTION

For electrolytes constituting electrochemical devices such as batteries,capacitors and sensors, liquid electrolytes have conventionally beenused from the viewpoint of ionic conductivity. They had however problemssuch as fear of these devices being damaged by liquid leak.

In order to overcome such a problem, secondary batteries using a solidelectrolyte such as inorganic crystalline material, inorganic glass ororganic polymer have recently been proposed. Compared with the use of aconventional liquid electrolyte employing a carbonate solvent, use ofsuch a solid electrolyte improves reliability and safety of the devicebecause it is free from the leak problem of the carbonate solvent andenables reduction in ignition property to an electrolyte.

Since organic polymers usually have excellent workability andmoldability or formability, can provide an electrolyte equipped withflexibility and bending property and heighten freedom of design of thedevice to which the resulting electrolyte is applied, they are expectedas a promising material.

Polymer electrolytes obtained by incorporating a specific alkali metalsalt in the organic polymers as described above, for example,polyethylene oxide however have an ionic conductivity lower than that ofthe liquid electrolytes and are therefore inferior thereto (for example,Z. Stoeva et al., J. Am. Chem. Soc. 125, 4619 (2003)).

In addition, in the polymer electrolytes, the alkali metal saltincorporated therein dissociates into a cation portion and an anionportion and respective ions transfer, but their selectivity plays animportant factor. In particular, when polymer electrolytes are appliedto lithium ion batteries, a higher transference number of lithium ionsis desired. Improvement in the transference number of lithium ionshowever decreases ionic conductivity, making it difficult to apply it tolithium ion batteries (for example, M. A. Mehta, et al., J. PowerSources, 81-82, 724 (1999).

An object of the present invention is to provide an ionic-conductivepolymer electrolyte satisfactory in both ionic conductivity andtransference number of lithium ion and a novel polymerizable boriccompound useful as a raw material for the ionic-conductive polymerelectrolyte.

SUMMARY OF THE INVENTION

In the present invention, there are thus provided a polymerizable boriccompound represented by the below-described formula (1) and anionic-conductive polymer electrolyte.

Use of the above-described compound or ionic-conductive polymerelectrolyte containing a polymer available by polymerizing apolymerizable composition containing the compound decreases the numberof moles of oxyalkylene groups added, facilitates transfer of lithiumions forming a coordinate bond to ether oxygen, and heightens ionicconductivity. In addition, a boron atom is fixed to a polymer matrix sothat the transference number of cation increases.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an expanded perspective view illustrating the constitution ofa lithium second battery for test using the polymer electrolyte of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the formula (1), Z represents a polymerizable functional group, forexample, a group having a polymerizable double bond such as vinyl,allyl, methallyl, acryloyl or methacryloyl. By selecting a group havinga polymerizable double bond and carrying out polymerization, anionic-conductive polymer or polymer electrolyte is available. Of theabove-described groups, vinyl, acryloyl and methacryloyl groups arepreferred because each of them can form a polymer readily by radicalpolymerization.

The above-described polymerizable boric compound for electrochemicaldevices can be produced by reacting a compound of the formula (2) withcompounds of the formulas (3) and (4).

In the formula, B represents a boron atom, Z represents a polymerizablefunctional group, X may be present or absent and represents a divalentC₁₋₁₂ hydrocarbon group, or in the absence of X, Z and B form a directbond, R^(a) and R^(b) each independently represents a C₁₋₂₄ hydrocarbongroup or a hydrogen atom, AO represents a C₂₋₄ oxyalkylene group, m andn each independently stands for 2 or greater but less than 6, and R¹ andR² represents a C₁₋₁₂ hydrocarbon group, with the proviso that theformula (3) and the formula (4) may be the same or different.

In the above-described producing method, it is preferred to select theconditions under which the total amount of the compounds of the formula(3) and formula (4) is from 1.5 to 2.1 moles per mole of the compound ofthe formula (2), and the reaction temperature falls within a range offrom 0 to 100° C.

In the formula (1), (3) or (4), R¹ and R² each represents aC₁₋₁₂hydrocarbon group. Examples of the C₁₋₁₂hydrocarbon group includealiphatic hydrocarbon groups such as methyl, ethyl, propyl, isopropyl,butyl, isobutyl, t-butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl,decyl, undecyl and dodecyl, aromatic hydrocarbon groups such as phenyl,toluyl and naphthyl, and alicyclic hydrocarbon groups such ascyclopentyl, cyclohexyl, methylcyclohexyl and dimethylcyclohexyl. Ofthese hydrocarbon groups, those having 4 or less carbon atoms arepreferred because they can increase the solubility of the electrolyticsalt, with a methyl group which is a C₁ hydrocarbon group being morepreferred. R¹ and R² may be the same or different.

In the formula (1) or (2), X represents a C₁₋₁₂ hydrocarbon group. WhenX is absent, B and Z form a direct bond. Examples of the C₁₋₁₂hydrocarbon group include aliphatic hydrocarbon groups such asmethylene, ethylene, propylene, isopropylene, butylene, isobutylene,dimethylethylene, pentylene, hexylene, heptylene, octylene, isooctylene,decylene, undecylene, and dodecylene, alicyclic hydrocarbon groups suchas cyclohexylene and dimethylcyclohexylene, and aromatic hydrocarbongroups such as phenylene, 2-methylphenylene, 2,6-dimethylphenylene and2-ethylphenylene. In order to increase a boron concentration to heightenthe transference number of cation, C₁₋₈ hydrocarbon groups arepreferred, with C₁₋₄ hydrocarbon groups being more preferred.

In the formula (1), (3) or (4), AO represents a C₂₋₄ oxylakylene groupsuch as oxyethylene, oxypropylene oxybutylene or oxytetramethylene. Useof an oxyethylene or oxypropylene group is preferred because it canheighten the ionic conductivity.

In the formula (1), (3) or (4), m and n each represents the number ofmoles of an oxyalkylene group added and each independently stands for 2or greater but less than 6. When m or n exceeds 6, mutual action withcation due to ether oxygen becomes large, leading to reduction in ionicconductivity.

The polymerizable boric compound of the formula (1) can be produced inthe following manner. It is available by adding a polyalkylene glycolmonoether represented by the formula (3) or (4) to a boric compound ofthe formula (2) having a polymerizable functional group and reacting themixture while feeding with dry air or nitrogen.

The total amount of the polyalkylene glycol monoethers represented bythe formulas (3) and (4) falls within a range of from 1.5 to 2.1 molesper mole of the boric compound of the formula (2) having a polymerizablefunctional group. In order to produce the polymerizable boric compoundof the formula (1) according to the present invention in a high yield,the total amount of the polyalkylene glycol monoethers represented bythe formulas (3) and (4) preferably falls within a range of from 1.8 to2.1 moles.

The compound of the formula (1) is produced by the reaction between thecompound of the formula (2) and the compounds of the formulas (3) and(4). The above-described reaction is an equilibrium reaction so that thereaction proceeds by the removal of the reaction by-product of theformula (5). When the compound to be eliminated is water (R^(a), R^(b):H), it can be eliminated by using toluene as a reaction solvent andutilizing azeotropy between the toluene and water. When the compound tobe eliminated is an alcohol (R^(a), R^(b): hydrocarbon group), it isvolatilized by vacuuming in an azeotropic mixture system by making useof a difference in boiling point and eliminated from the reactionsystem. When the compound to be eliminated is an alcohol, a reactionsolvent such as toluene can also be used. The reaction temperature isfrom 0 to 100° C., with from 0 to 80° C. being preferred for the purposeof avoiding initiation of polymerization of the polymerizable functionalgroup which will otherwise occur owing to thermal history.

wherein,

the formula (2): a boric compound having a polymerizable functionalgroup (in which B represents a boron atom, Z represents a polymerizablefunctional group, X represents a divalent C₁₋₁₂ hydrocarbon group orphenylene group, or in the absence of X, Z and B form a direct bond, andR^(a) and R^(b) each independently represents a C₁₋₂₄ hydrocarbon groupor hydrogen atom),

the formulas (3) and (4): polyalkylene glycol monoethers (in which AOrepresents a C₂₋₄ oxyalkylene group, m and n each independently standsfor 2 or greater but less than 6, and R¹ and R² each represents a C₁₋₁₂hydrocarbon group, with the proviso that the formulas (3) and (4) may bethe same or different),

the formula (1): polymerizable boric compound, and

the formula (5): water or alcohol.

The polymerizable boric compound of the formula (1) may be polymerizedby any one of the conventionally known methods, that is, bulkpolymerization, solution polymerization and emulsion polymerization.Another polymerization compound may be used in combination. Examples ofthe another polymerizable compound include compounds having a(meth)acrylate group, vinyl group or allyl group. From the viewpoints ofhandling ease and contribution to ionic conductivity, (meth)acrylatecompounds and polyalkylene glycol (meth)acrylate compounds arepreferred. A polymerization initiator is not indispensable for effectingpolymerization. From the viewpoint of handling ease, use of a radicalpolymerization initiator is preferred.

Polymerization in the presence of a radical polymerization initiator canbe carried out while employing ordinarily employed conditions intemperature range and polymerization time. In order not to impairmembers to be used for an electrochemical device, it is preferred to usea radical polymerization initiator having from 30 to 90° C. as a rangeof 10-hour half-life temperature which is an indicator of decompositiontemperature and rate. The term “10-hour half-life temperature” means atemperature necessary for reduction, by half, of the amount of anundecomposed radical polymerization initiator having a concentration of0.01 mole/liter in a radical inert solvent such as benzene in 10 hours.The amount of the initiator in the present invention is 0.01 mol % orgreater but not greater than 10 mol %, preferably 0.1 mol % or greaterbut not greater than 5 mol %, per mol of the polymerizable functionalgroup.

Examples of the radical polymerization initiators include organicperoxides such as t-butyl peroxypivalate, t-hexyl peroxypivalate, methylethyl ketone peroxide, cyclohexanone peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,2-bis(t-butylperoxy)octane, n-butyl-4,4-bis(t-butylperoxy)valerate,t-butyl hydroperoxide, cumene hydroperoxide,2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide,t-butylcumyl peroxide, dicumyl peroxide,a,a′-bis(t-butylperoxy-m-isopropyl)benzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, benzoyl peroxide andt-butylperoxyisopropyl carbonate, and azo compounds such as2,2′-azobisisobutyronitrile, 2,2′-azobis(2-methylbutyronitrile),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile),1,1′-azobis(cyclohexane-1-carbonitrile),2-(carbamoylazo)isobutyronitrile,2-phenylazo-4-methoxy-2,4-dimethyl-valeronitrile,2,2′-azobis(2-methyl-N-phenylpropionamidine) dihydrochloride,2,2′-azobis[N-(4-chlorophenyl)-2-methylpropionamidine]dihydrochloride,2,2′-azobis[N-hydroxyphenyl]-2-methylpropionamidine]dihydrochloride,2,2′-azobis[2-methyl-N-(phenylmethyl)propionamidine]dihydrochloride,2,2′-azobis[2-methyl-N-(2-propenyl)propionamidine]dihydrochloride,2,2′-azobis(2-methylpropionamidine) dihydrochloride,2,2′-azobis[N-(2-hydroxyethyl)-2-methylpropionamidine]dihydrochloride,2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride,2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl]propane],2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide},2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide},2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2′-azobis(2-methylpropionamide)dihydrate,2,2′-azobis(2,4,4-trimethylpentane), 2,2′-azobis(2-methylpropane),dimethyl 2,2′-azobisisobutyrate and 4,4′-azobis (4-cyanovaleric acid),and 2,2′-azobis[2-(hydroxymethyl)propionitrile.

Although no particular limitation is imposed on the electrolytic saltsused in the present invention insofar as they are soluble in thepolymerizable boric compound of the present invention or polymerobtained by polymerizing the compound, following ones are preferred.Examples include compounds composed of a metallic cation and an anionselected from chloride ion, bromide ion, iodide ion, perchlorate ion,thiocyanate ion, tetrafluoroborate ion, hexafluorophosphate ion,trifluoromethanesulfonideimidate ion, stearylsulfonate ion,octylsulfonate ion, dodecylbenzenesulfonate ion, naphthalenesulfonateion, dodecylnapthalenesulfonate ion, 7,7,8,8-tetracyano-p-quinodimethaneion, and lower aliphatic carboxylate ions. Examples of the metalliccation include Li, Na, K, Rb, Cs, Mg, Ca and Ba metallic ions.

Concentration of the electrolyte preferably falls within a range of from0.0001 to 1, more preferably from 0.001 to 0.5 as a molar ratio based onthe number of moles of ether oxygen atoms contained in the oxyalkylenegroup of the ion-conductive polymer, namely, (the number of moles ofelectrolytic salt)/(total number of moles of ether oxygen atomscontained in an oxyalkylene group). Molar ratios exceeding 1 lead todeteriorations in the workability, moldability or formability andmechanical strength of the resulting polymer electrolyte.

Examples of the plasticizer in the present invention include organicsolvents employed for electrolytes for lithium batteries such as diethylcarbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate,γ-butyrolactone, tetrahydrofuran and dimethoxyethane, and borate estercompounds. By adding such a compound to an ion-conductive polymerelectrolyte, physical properties of the electrolyte can be controlled asneeded.

Examples of the reinforcing material in the present invention includefibrous glass cloth using glass fibers, nonwoven fabric made ofpolyolefin, polyester or the like, and separators for lithium ionbatteries. Any material can be used insofar as it is a reinforcingmaterial not adversely affecting lithium batteries. Use of thereinforcing material increases the mechanical strength, enabling filmthinning of ion-conductive polymer electrolytes.

The polymer electrolyte according to the present invention is veryuseful as an electrolyte for secondary batteries, especially useful aselectrolyte for lithium secondary batteries.

EXAMPLES

The present invention will hereinafter be described more specifically byexamples. It should however be borne in mind that the present inventionis not limited to or by them. In the examples, preparation of samplesand evaluation of ionic conductivity were all carried out in an argonatmosphere. Moreover, in all the examples and comparative examples,concentration of the electrolytic salt was adjusted so that the molarratio based on the total number of moles of ether oxygen atoms in theoxyalkylene group in the ion-conductive polymer, that is, (the number ofmoles of electrolytic salt)/(total number of moles of ether oxygen atomsin oxyalkylene group) be 0.03. The examples and the comparative examplesin the present invention are listed in Table 1.

Method of Evaluation

<Ionic conductivity> The ionic conductivity was measured by analternating current impedance method which comprises putting a polymerelectrolyte between stainless steel electrodes at 25° C. to construct anelectrochemical cell and applying an alternating current between theelectrodes, and measuring the resistant components, and the ionicconductivity was calculated from real-number impedance intercept in aCole-Cole plot.<Transference number of lithium ion> The polymer electrolytes obtainedin the below-described Examples 1 to 7 and Comparative Examples 1 and 2were each sandwiched between lithium metals and the transference numberof lithium ion was measured in accordance with the method as describedin J. Evans, et. al., Polymer, 28, 2324 (1987). The results are shown inTable 1.

Example 1

To 504 g (2.0 mol) of pentaethylene glycol monomethyl ether was added184 g (1.0 mol) of dibutyl vinyl borate (product of Aldrich) from whicha polymerization inhibitor had been removed by distillation, followed bystirring at room temperature for 30 minutes. After the pressure in thesystem was reduced to 0.4 kPA, the temperature was raised to 55° C.Stirring was continued for 3 hours to remove eliminating butanol,whereby 432 g of a polymerizable boric compound A represented by theformula (1) (X: absent, m and n=5, R¹ and R²=methyl group) was obtained.As a result of observation by infrared absorption spectrometry, anabsorption band originating from hydroxyl group at 3300 cm⁻¹disappeared, from which the existence of the resulting polymerizableboric compound A was confirmed.

A polymerizable composition was obtained by mixing 5.40 g (10 mmol) ofthe polymerizable boric compound A, 5.40 g of2,2′-azobisisobutyronitrile and LiN(CF₃SO₂)₂ as an electrolytic salt.The resulting solution was poured into a boat made ofpolytetrafluoroethylene and kept at 80° C. for 3 hours to obtain apolymer electrolyte of 0.1 mm thickness. The film of the electrolytethus obtained was cut into a disc of 1 cm in diameter, and put between apair of stainless steel electrodes. The ionic conductivity was thendetermined by the above-described measuring method of ionic conductivityat 25° C. The ionic conductivity was found to be 0.5 mS/cm.

Example 2

To 328 g (2.0 mol) of triethylene glycol monomethyl ether was added 184g (1.0 mol) of dibutyl vinyl borate (product of Aldrich) from which apolymerization inhibitor had been removed by distillation, followed bystirring at room temperature for 30 minutes. After the pressure in thesystem was reduced to 0.4 kPA, the temperature was raised to 60° C.Stirring was continued for 3 hours to remove eliminating butanol,whereby 273 g of a polymerizable boric compound B represented by theformula (1) (X: absent, m and n=3, R¹ and R²=methyl group) was obtained.As a result of observation by infrared absorption spectrometry, anabsorption band originating from hydroxyl group at 3300 cm⁻¹disappeared, from which the existence of the resulting polymerizableboric compound B was confirmed.

A polymerizable composition was obtained by mixing 3.64 g (10 mmol) ofthe polymerizable boric compound B, 3.64 mg of2,2′-azobisisobutyronitrile and LiN(CF₃SO₂)₂ as an electrolytic salt.The resulting solution was poured into a boat made ofpolytetrafluoroethylene and kept at 80° C. for 3 hours to obtain apolymer electrolyte of 0.1 mm thickness. The film of the electrolytethus obtained was cut into a disc of 1 cm in diameter, and put between apair of stainless steel electrodes. The ionic conductivity was thendetermined by the above-described measuring method of ionic conductivityat 25° C. The ionic conductivity was found to be 1.0 mS/cm.

Example 3

To 504 g (2.0 mol) of pentaethylene glycol monomethyl ether was added148 g (1.0 mol) of 4-vinylphenyl boric acid (product of Aldrich),followed by the addition of toluene as a solvent. After the pressure inthe system was reduced to 8 kPA, the temperature was raised to 55° C.Stirring was continued for 5 hours under toluene reflux to remove waterwhich was a reaction by-product. The toluene as a solvent was thendistilled off, whereby 246 g of a polymerizable boric compound Crepresented by the formula (1) (X=phenylene, m and n=5, R¹ and R²=methylgroup) was obtained. As a result of observation by infrared absorptionspectrometry, an absorption band originating from hydroxyl group at 3300cm⁻¹ disappeared, from which the existence of the resultingpolymerizable boric compound C was confirmed.

A polymerizable composition was obtained by mixing 6.16 g (10 mmol) ofthe polymerizable boric compound C, 6.16 mg of2,2′-azobisisobutyronitrile and LiN(CF₃SO₂)₂ as an electrolytic salt.The resulting solution was poured into a boat made ofpolytetrafluoroethylene and kept at 100° C. for 3 hours to obtain apolymer electrolyte of 0.1 mm thickness. The film of the electrolytethus obtained was cut into a disc of 1 cm in diameter, and put between apair of stainless steel electrodes. The ionic conductivity was thendetermined by the above-described measuring method of ionic conductivityat 25° C. The ionic conductivity was found to be 0.08 mS/cm.

Example 4

To 328 g (2.0 mol) of triethylene glycol monomethyl ether was added 148g (1.0 mol) of 4-vinylphenyl boric acid (product of Aldrich), followedby the addition of toluene as a solvent. After the pressure in thesystem was reduced to 8 kPA, the temperature was raised to 55° C.Stirring was continued for 5 hours to remove water which was a reactionby-product. The toluene as a solvent was then distilled off, whereby 220g of a polymerizable boric compound D represented by the formula (1)(X=phenylene, m and n=3, R¹ and R=methyl group) was obtained. As aresult of observation by infrared absorption spectrometry, an absorptionband originating from hydroxyl group at 3300 cm⁻¹ disappeared, fromwhich the existence of the resulting compound D was confirmed.

A polymerizable composition was obtained by mixing 4.40 g (10 mmol) ofthe polymerizable boric compound D, 4.40 mg of2,2′-azobisisobutyronitrile and LiN(CF₃SO₂)₂ as an electrolytic salt.The resulting solution was poured into a boat made ofpolytetrafluoroethylene and kept at 100° C. for 3 hours to obtain apolymer electrolyte of 1 mm thickness. The film of the electrolyte thusobtained was cut into a disc of 1 cm in diameter, and put between a pairof stainless steel electrodes. The ionic conductivity was thendetermined by the above-described measuring method of ionic conductivityat 25° C. The ionic conductivity was found to be 0.05 mS/cm.

Example 5

As in Example 4, a polymerizable composition solution was obtained byadding 0.5 g of propylene carbonate to a solution obtained by mixing4.40 g (10 mmol) of the polymerizable compound D, 4.40 mg of2,2′-azobisisobutyronitrile and LiN(CF₃SO₂)₂. The resulting solution waspoured into a boat made of polytetrafluoroethylene and kept at 100° C.for 3 hours to obtain a polymer electrolyte of 1 mm thickness. The filmof the electrolyte thus obtained was cut into a disc of 1 cm indiameter, and put between a pair of stainless steel electrodes. Theionic conductivity was then determined by the above-described measuringmethod of ionic conductivity at 25° C. The ionic conductivity was 0.4mS/cm.

Example 6

As in Example 4, a polymerizable composition solution was obtained bymixing 4.40 g (10 mmol) of the polymerizable compound D, 4.40 mg of2,2′-azobisisobutyronitrile and LiN(CF₃SO₂)₂. With the resultingsolution, a glass cloth (50 μm thickness) to be used as a reinforcingmaterial was impregnated and the resulting cloth was maintained at 100°C. for 3 hours, whereby a polymer electrolyte of 70 μm thickness wasobtained. The film of the electrolyte thus obtained was cut into a discof 1 cm in diameter, and put between a pair of stainless steelelectrodes. The ionic conductivity was then determined by theabove-described measuring method of ionic conductivity at 25° C. Theelectrolyte film was found to have ionic conductivity of 0.04 mS/cm, andin addition, had excellent strength.

Example 7

In a substantially similar manner to Example 6 except for the use of apolyolefin nonwoven fabric (50 μm thickness) as a reinforcing material,a polymer electrolyte of 60 μm thickness was obtained. The ionconductivity of the resulting electrolyte was determined by a similarmeasuring method. The resulting electrolyte film showed an ionconductivity of 0.04 mS/cm and in addition, had excellent strength.

Comparative Example 1

After polyethylene oxide (product of Fluka, 98%, average molecularweight: 1000) was dried by allowing it to stand for 4 days at 30° C.under reduced pressure of 1.3 kPa, it was dissolved in acetonitrile ofthe same amount to give a corresponding polymer solution. To theresulting polymer solution was added LiPF₆ in an amount to give a molarratio (the number of moles of electrolytic salt)/(the total number ofmoles of ether oxygen atoms in polyethylene oxide) of 0.17 relative tothe total number of moles of ether oxygen atoms of polyethylene oxide.Acetonitrile was distilled off from the solution to obtain a powderhaving an Li ion coordinated in polyethylene oxide. An electrolyte filmwas prepared by pressing the resulting powder. As a result ofmeasurement, its ion conductivity was then found to be 6.3×10⁻⁸ S/cm at25° C., which was lower than that of any one of the electrolytesobtained in Examples.

Comparative Example 2

A boroxin-ring-having polymer electrolyte represented by thebelow-described formula (6) was obtained by adding 770 g (2.2 mol) ofpolyethylene glycol monomethyl ether having a molecular weight of 350(product of Aldrich), 310 g (1.6 mol) of tetraethylene glycol (productof Aldrich) and lithium chloride to 3 mol of boric anhydride and heatingto remove water which was the reaction by-product. The amount of lithiumchloride was adjusted so that a molar ratio of a lithiumchloride/boroxin ring of the boroxin compound thus formed be 0.5/1. As aresult of measurement, the polymer electrolyte had an ion conductivityof 3.3×10⁻⁸ S/cm at 25° C. and the transference number of Li ion was0.88. The ion conductivity was lower than that of any one of theelectrolytes obtained in Examples.

Examples and Comparative Examples so far described were summarized inTable 1. The polymer electrolytes according to the present invention areeffective as an electrolyte for secondary batteries, particularly as anelectrolyte for lithium secondary batteries.

TABLE 1

Ion Transference conductivity number of Ex. X m n Kind of salt (mS/cm)lithium ion 1 Absent 5 5 LiN(CF₃SO₂)₂ 0.5 0.56 2 Absent 3 3 LiN(CF₃SO₂)₂1.0 0.51 3 Phenylene 5 5 LiN(CF₃SO₂)₂ 0.08 0.52 4 Phenylene 3 3LiN(CF₃SO₂)₂ 0.05 0.50 5 Phenylene 3 3 LiN(CF₃SO₂)₂ 0.4 0.20 6 Phenylene3 3 LiN(CF₃SO₂)₂ 0.04 0.45 7 Phenylene 3 3 LiN(CF₃SO₂)₂ 0.04 0.45 Comp.— LiPF₆ 0.000025 — Ex. 1 Comp. — LiN(CF₃SO₂)₂ 0.0006 0.88 Ex. 2

Examples of a positive electrode which reversibly intercalates anddeintercalates lithium in a lithium secondary battery include laminarcompounds such as lithium cobaltate (LiCoO₂) and lithium nickelate(LiNiO₂), the above compounds substituted with one or more transitionmetals, and mixtures containing a lithium manganate [Li_(1+x)Mn_(2−x)O₄(x=from 0 to 0.33), Li_(1+x)Mn_(2−x−y)M_(y)O₄ (in which M includes atleast one metal selected from Ni, Co, Cr, Cu, Fe, Al and Mg, x=from 0 to0.33, y=from 0 to 1.0, and 2−x−y>0), LiMnO₃, LiMn₂O₃, LiMnO₂,LiMn_(2−x)M_(x)O₂ (in which, M includes at least one metal selected fromCo, Ni, Fe, Cr, Zn and Ta, and x=from 0.01 to 0.1), Li₂Mn₃MO₈ (in which,M includes at least one metal selected from Fe, Co, Ni, Cu and Zn)],copper-lithium oxide (Li₂CuO₂), a vanadium oxide such as LiV₃O₈,LiFe₃O₄, V₂O₅ or Cu₂V₂O₇, a disulfide compound, or Fe₂ (MoO₄)₃.

As a negative electrode which reversibly intercalates and deintercalateslithium in a lithium secondary battery, usable are materials obtained byheat treating a natural graphite or a readily graphitizable materialavailable from petroleum cokes, coal pitch cokes or the like at atemperature as high as 2500° C. or greater, mesophase carbon, amorphouscarbon, carbon fibers, metals capable forming an alloy with lithium, andmaterials having a metal supported on the surface of carbon particles.Examples include metals selected from lithium, silver, aluminum, tin,silicon, indium, gallium and magnesium, and alloys thereof. Furthermore,these metals or oxides of them can be utilized as a negative electrode.

Although uses of the lithium ion secondary batteries of the presentinvention are not particularly limited, they can be used, for example,as power sources of IC cards, personal computers, large-sized electroniccomputers, notebook type personal computers, pen input personalcomputers, notebook type word processors, cellular phones, portablecards, watches, cameras, electric shavers, cordless phones, facsimiles,video, video cameras, electronic pocketbooks, desk electric calculators,electronic pocketbooks with communication functions, portable copyingmachines, liquid crystal televisions, electric tools, cleaners, gamedevices having functions such as virtual reality, toys, electricbicycles, walk assisting machines for medical care, wheelchairs formedical care, moving beds for medical care, escalators, elevators,forklifts, golf carts, power sources for emergency, load conditionersand power storage systems. Furthermore, they can be used for public useand also for war use and space use.

The present invention will hereinafter be described more specifically byexamples. It should however be borne in mind that the present inventionis not limited to or by them. In the examples, preparation of samplesand evaluation of ionic conductivity were all carried out in an argonatmosphere unless otherwise specified. Moreover, in all the examples andcomparative examples, concentration of the electrolytic salt wasadjusted so that the molar ratio based on the total number of moles ofether oxygen atoms in the oxyalkylene group in the ion conductivepolymer [(the number of moles of electrolytic salt)/(the total number ofmoles of ether oxygen atoms in oxyalkylene group)] be 0.03.

The polymer electrolytes used in Examples 8 to 13 are those prepared inExamples 1 to 7 and electrolytic salts are similar to those employed inExamples 1 to 6. Accordingly, Example 1, Example 2 and Examples 3 to 6correspond to Example 8, Example 9 and Examples 10 to 13, respectively.The polymer electrolyte used in Comparative Example 3 is that preparedin Comparative Example 1, while the electrolytic salt of ComparativeExample 3 is similar to that used in Comparative Example 1.

1. Preparation Examples of Electrodes

<Positive electrode> “CELLSEED” (trade name of lithium cobaltate;product Nippon Chemical Industrial Co., Ltd.), “SP270” (trade name ofgraphite; product of Japan Graphite Co., Ltd.) and “KF1120” (trade nameof polyvinylidene fluoride; product of Kureha Chemical Industry Co.,Ltd.) were mixed at a ratio of 80:10:10 in % by weight, and the mixturewas poured into N-methyl-2-pyrrolidone, followed by mixing to prepare aslurry solution. The resulting slurry was coated on an aluminum foil of20 μm thickness by the doctor blade method and dried. The coating amountof the mixture was 150 g/m². The aluminum foil was pressed to give amixture bulk density of 3.0 g/cm³ and cut into 1 cm×1 cm to prepare apositive electrode. <Negative electrode> “CARBOTRON PE” (trade name ofamorphous carbon; product of Kureha Chemical Industry Co., Ltd.) and“KF1120” (trade name of polyvinylidene fluoride; product of KurehaChemical Industry Co., Ltd.) were mixed at a ratio of 90:10 in % byweight, and the mixture was poured into N-methyl-2-pyrrolidone, followedby mixing to prepare a slurry solution. The resulting slurry was coatedon a copper foil of 20 μm thickness by the doctor blade method anddried. The coating amount of the mixture was 70 g/m². The resultingcopper foil was pressed to give a mixture bulk density of 1.0 g/cm³, andcut into 1.2 cm×1.2 cm to prepare a negative electrode.1. Method of Evaluation<Charging and discharging conditions of battery> Charging anddischarging were carried out at 25° C. and at a current density of 0.5mA/cm² by using a charging and discharging device (“TOSCAT 3000”, tradename; product of Toyo System Co., Ltd.). A constant current charging wascarried out up to 4.2 V, and after the voltage reached 4.2 V, a constantvoltage charging was carried out for 12 hours. Furthermore, a constantcurrent discharging was carried out until a cut-off voltage of dischargereached 3.5 V. The capacity obtained by the first discharging was takenas an initial charge/discharge capacity.Charging-discharging under the above conditions was regarded as 1 cycle,and the charging and the discharging were repeated until the capacitydecreased to 70% or lower of the initial discharge capacity, and thenumber of repetition was taken as cycle characteristic. Furthermore, aconstant current charging was carried out at a current density of 1mA/cm² up to 4.2 V, and after the voltage reached 4.2 V, a constantvoltage charging was carried out for 12 hours. Furthermore, a constantcurrent discharging was carried out until a cut-off voltage of dischargereached 3.5 V. The resulting capacity and the initial cycle capacityobtained by the above charge and discharge cycle were compared, and theratio was taken as a high-rate charge and discharge characteristics.

Example 8

The polymerizable composition solution obtained in Example 1 was castover the positive electrode and negative electrode prepared by theabove-described method and kept at 80° C. for 6 hours, whereby a polymerelectrolyte was prepared thereover. These positive electrode andnegative electrode were stacked one after another and kept at 80° C. for6 hours under a load of 0.1 MPa. As illustrated in FIG. 1, stainlesssteel terminals 5 and 6 were then attached to positive electrode 1 andnegative electrode 2, and they were inserted in a bag-shaped aluminumlaminate film 7. The initial charge/discharge capacity of the batterythus obtained was 0.5 mAh, and the cycle characteristic was 50 times.The high rate discharge characteristic was 81%. When the aluminumlaminate film was peeled off the battery, no fluidity of the electrolytewas observed inside the battery.

Example 9

The polymerizable composition solution obtained in Example 2 was castover the positive electrode and negative electrode prepared by theabove-described method and kept at 80° C. for 6 hours, whereby a polymerelectrolyte was prepared thereover. These positive electrode andnegative electrode were stacked one after another and adhered by keepingthem at 80° C. for 6 hours under a load of 0.1 MPa. As illustrated inFIG. 1, stainless steel terminals 5 and 6 were then attached to positiveelectrode 1 and negative electrode 2, and they were inserted in abag-shaped aluminum laminate film 7. The initial charge/dischargecapacity of the battery thus obtained was 0.7 mAh, and the cyclecharacteristic was 70 times. The high rate discharge characteristic was90%. When the aluminum laminate film was peeled off the battery, nofluidity of the electrolyte was observed inside the battery.

Example 10

The polymerizable composition solution obtained in Example 3 was castover the positive electrode and negative electrode prepared by theabove-described method and kept at 80° C. for 6 hours, whereby a polymerelectrolyte was prepared thereover. These positive electrode andnegative electrode were stacked one after another and adhered by keepingthem at 80° C. for 6 hours under a load of 0.1 MPa. As illustrated inFIG. 1, stainless steel terminals 5 and 6 were then attached to positiveelectrode 1 and negative electrode 2, and they were inserted in abag-shaped aluminum laminate film 7. The initial charge/dischargecapacity of the battery thus obtained was 0.3 mAh, and the cyclecharacteristic was 30 times. The high rate discharge characteristic was50%. When the aluminum laminate film was peeled off the battery, nofluidity of the electrolyte was observed inside the battery.

Example 11

The polymerizable composition solution obtained in Example 4 was castover the positive electrode and negative electrode prepared by theabove-described method and kept at 80° C. for 6 hours, whereby a polymerelectrolyte was prepared thereover. These positive electrode andnegative electrode were stacked one after another and adhered by keepingthem at 80° C. for 6 hours under of a load of 0.1 MPa. As illustrated inFIG. 1, stainless steel terminals 5 and 6 were then attached to positiveelectrode 1 and negative electrode 2, and they were inserted in abag-shaped aluminum laminate film 7. The initial charge/dischargecapacity of the battery thus obtained was 0.45 mAh, and the cyclecharacteristic was 40 times. The high rate discharge characteristic was75%. When the aluminum laminate film was peeled off the battery, nofluidity of the electrolyte was observed inside the battery.

Example 12

The polymerizable composition solution obtained in Example 5 was castover the positive electrode and negative electrode prepared in theabove-described method and kept at 80° C. for 6 hours, whereby a polymerelectrolyte was prepared thereover. These positive electrode andnegative electrode were stacked one after another and adhered by keepingthem at 80° C. for 6 hours under a load of 0.1 MPa. As illustrated inFIG. 1, stainless steel terminals 5 and 6 were then attached to positiveelectrode 1 and negative electrode 2, and they were inserted in abag-shaped aluminum laminate film 7. The initial charge/dischargecapacity of the battery thus obtained was 0.5 mAh, and the cyclecharacteristic was 50 times. The high rate discharge characteristic was80%. When the aluminum laminate film was peeled off the battery, nofluidity of the electrolyte was observed in the battery.

Example 13

The polymerizable composition solution obtained in Example 6 was castover the positive electrode and negative electrode prepared by theabove-described method and kept in an atmosphere of pressure of 0.4 kPaand temperature of 80° C. for 6 hours to distill off the solvent,acetonitrile, whereby a polymer electrolyte was prepared over thepositive and negative electrodes. The resulting positive electrode andnegative electrode were stacked one after another and adhered by keepingthem at 80° C. for 6 hours under a load of 0.1 MPa. As illustrated inFIG. 1, stainless steel terminals 5 and 6 were then attached to positiveelectrode 1 and negative electrode 2, and they were inserted in abag-shaped aluminum laminate film 7. The initial charge/dischargecapacity of the battery thus obtained was 0.5 mAh, and the cyclecharacteristic was 50 times. The high rate discharge characteristic was80%. When the aluminum laminate film was peeled off the battery, nofluidity of the electrolyte was observed inside the battery.

Comparative Example 3

The polymerizable composition solution obtained in Comparative Example 1was cast over the positive electrode and negative electrode prepared bythe above-described method and kept in an atmosphere of pressure of 0.4kPa and temperature of 80° C. for 6 hours to distill off acetonitrilefrom the solution, whereby an electrolyte was prepared over the positiveelectrode and negative electrode. The resulting positive electrode andnegative electrode were stacked one after another and adhered by keepingthem at 80° C. for 6 hours under a load of 0.1 MPa. As illustrated inFIG. 1, stainless steel terminals 5 and 6 were then attached to positiveelectrode 1 and negative electrode 2, and they were inserted in abag-shaped aluminum laminate film 7. It was however impossible to carryout charging and discharging evaluation, at 25° C., of the battery thusprepared.

TABLE 2 high rate discharge Initial Cycle characteristic (%)charge/discharge characteristic Current density Examples capacity (mAh)(times) (1.0 mA/cm²) 8 0.5 50 81 9 0.7 70 90 10 0.3 30 50 11 0.45 40 7512 0.5 50 80 13 0.5 50 80 Comp. 0 0 0 Ex. 3

The present invention is very useful when applied to lithium secondarybatteries as described below.

(1) A lithium secondary battery equipped with positive and negativeelectrodes which reversibly intercalate and deintercalate lithium, andan electrolyte containing an ion conductive substance and anelectrolytic salt, wherein the ion conductive substance is composed of apolymerizable boric compound represented by the formula (1).

(2) A lithium secondary battery, wherein the electrolyte is composed ofa polymer obtained by polymerizing a polymerizable boric compoundrepresented by the formula (1).

(3) A lithium second battery, wherein the electrolyte is composed of apolymer available by polymerizing a polymerizable boric compoundrepresented by the formula (1) and a plasticizer.

(4) A lithium second battery, wherein the electrolytic salt is at leastone of LiPF₆, LiN(CF₃SO₂)₂, LiClO₄, LiBF₄, LiAsF₆, LiI, LiBr, LiSCN,Li₂B₁₀Cl₁₀, and LiCF₃SO₃.

(5) A lithium secondary battery, wherein the electrolyte has beenretained by a reinforcing material.

1. A polymerizable composition for electrochemical devices, whichcomprises an electrolytic salt and a polymerizable boric compound forelectrochemical devices represented by the formula (1):

wherein, B represents a boron atom, Z represents a polymerizablefunctional group selected from the group consisting of vinyl, allyl,methallyl, acryloyl and methacryloyl, X represents a divalent C₁₋₁₂hydrocarbon group, or Z and B form a direct bond in the absence of X, AOrepresents a C₂₋₄ oxyalkylene group, m and n are each the number ofmoles of the oxyalkylene group added and each independently stands for 2or greater but less than 6, and R¹ and R² each represents a C₁₋₁₂hydrocarbon group.
 2. A polymer electrolyte for electrochemical devicesavailable by polymerizing a polymerizable composition as claimed inclaim
 1. 3. A polymer electrolyte for electrochemical devices accordingto claim 2, which comprises a plasticizer.
 4. A polymer electrolyteaccording to claim 3, wherein the electrolytic salt is at least one ofLiPF₆, LiN(CF₃SO₂)₂, LiClO₄, LiBF₄, LiAsF₆, Lil, LiBr, LiSCN,Li₂B₁₀Cl₁₀, and LiCF₃SO₃.
 5. A secondary battery comprising a positiveelectrode having a terminal, a negative electrode having a terminal, anda polymer electrolyte as claimed in claim 3 sandwiched between saidpositive electrode and said negative electrode, the polymer electrolytecontaining the electrolytic salt.
 6. A polymer electrolyte according toclaim 2, wherein the electrolytic salt is at least one of LiPF₆,LiN(CF₃SO₂)₂, LiClO₄, LiBF₄, LiAsF₆, Lil, LiBr, LiSCN, Li₂B₁₀Cl₁₀, andLiCF₃SO₃.
 7. A secondary battery comprising a positive electrode havinga terminal, a negative electrode having a terminal, and a polymerelectrolyte as claimed in claim 6 sandwiched between said positiveelectrode and said negative electrode, the polymer electrolytecontaining the electrolytic salt.
 8. A polymer electrolyte forelectrochemical devices according to claim 2, which has been retained ina reinforcing material.
 9. A secondary battery comprising a positiveelectrode having a terminal, a negative electrode having a terminal, anda polymer electrolyte as claimed in claim 8 sandwiched between saidpositive electrode and said negative electrode, the polymer electrolytecontaining the electrolytic salt.
 10. A secondary battery comprising apositive electrode having a terminal, a negative electrode having aterminal, and a polymer electrolyte as claimed in claim 2 sandwichedbetween said positive electrode and said negative electrode, the polymerelectrolyte containing the electrolytic salt.